Grade 11General Physics

The 15 que asking me the velocity at 4s
If we differentiate x we get velocity as 61 m/s but when we but value of t as 4 in eq of x we get 134 m and by further dividing it by 4 we get velocity as 33.5 m/s ....why there is a difference....plz help me

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Preet Tripathi

5 Years agoGrade 11

1 Answer

Tanishq Gupta

5 Years ago

Hello Preet,

The velocity that you have calculated by differenciating ‘x’ with respect to time is absolutely correct that is 61 m/s.

Now as mentioned in the question the particle is in uniform acceleration motion so therefore in the condition of acceleration motion we cannot apply the formula ‘velocity = displacement / time’ for that the velocity must be constant.

Instead in the condition of acceleration motion we have to apply the equation of motion.

Verification : x=2+5t+7t²

initial velocity (u) = 5 m/s (at t=0)

acceleration (at t=4) = 14 m/s²

by 1^st equation of motion : v=u+at

v=5+14(4)

v=61 m/s

Hence Proved.

Hope you find it useful.

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The 15 que asking me the velocity at 4sIf we differentiate x we get velocity as 61 m/s but when we but value of t as 4 in eq of x we get 134 m and by further dividing it by 4 we get velocity as 33.5 m/s ....why there is a difference....plz help me

Preet Tripathi

1 Answer

Tanishq Gupta

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The 15 que asking me the velocity at 4s
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